Calibration of IQ imbalance in OFDM transceivers

High rate wireless communication systems require the design of low-cost radio transceivers with low power consumption. The design of direct conversion receivers, which convert the radio frequency directly to baseband, has thus been the subject of active investigation in recent years. However, such architectures introduce certain design challenges of their own, namely DC offsets as well as gain and phase mismatches in the in-phase and quadrature paths. In this paper, we propose novel methods for calibrating the IQ imbalance in the receiver for OFDM communication systems. Relations are derived for the estimation of the gain and phase parameters for AWGN as well as frequency selective fading channels. We will also investigate the statistical properties of the estimated parameters. The calibration procedure is verified for an OFDM system designed based on the IEEE 802.11a standard for wireless local area networks.